Wow, so I guess a meter isn't always a good meter? Then again music is a fluid science not a mathematical one. I've heard of software that could do the same thing. Does anybody know how reliable these are and what is needed?

I am just trying to get a feel for the SPL in my room when I record guitar. Whether or not I am endangering my hearing or not and etc.

BTW: No I don't crank the amps up as a starting point for recording, but loud enough. (I've read the Slipperman article, so I use that as a foundation.)

You should be able to find a fairly reliable one for $50 or thereabouts.

I've had an old analog one from Radio Shack that I got back in the early 80's - It still works like a champ. I have a cute cheap little digital $30 - one of the ±3.5dB deals. And I have a Phonic PAA3 that I use a lot in my day to day work.

The problem you'll have with any software meter is, what would you calibrate it to? You need a calibrated mic and specifically calibrated amp.

Do your ears ring after you've been playing guitar for a while? If they do, it's a warning.
Safe exposure is a combination of sound level and duration. It's cumulative, so the older you get the worse it will get.

Here's a graph of OSHA's recommended maximum exposure:

http://www.etymotic.com/ephp/erme-ihp.aspx

ALSO: If you play live, I'm a big fan of the Westone or Etymotic Research ER15 custom molded earplugs. They're not cheap, but I'd probably be deaf as a post if I hadn't started wearing them almost 20 years ago.